1. Field of the Invention
The present invention relates generally to a method and waveguides for changing the direction of longitudinal vibrations, and more particularly pertains to a method and waveguides for changing the direction of longitudinal vibrations which maintain efficiency of operation over a larger angle of change than prior art designers typically accepted as possible.
2. Discussion of the Prior Art
In the design of acoustic or electromagnetic waveguides it is widely believed that sharp turns in a waveguide lead to inefficiencies of parasitic motion, excessive heat generation and noise. A common rule of thumb holds that a radius of curvature of a waveguide should not be less than the transmitted wavelength because a smaller radius of curvature causes the efficiency of the waveguide to quickly drop below 100%. A cutoff radius occurs at approximately one-sixth the wavelength. Designers define a cutoff radius R by the equation R greater than xcex/2xcfx80, where xcex represents the wavelength of the transmitted energy and xcfx80 is the well-known ratio of the circumference of any circle to its diameter, or approximately 3.14.
Prior art waveguide designs avoided having a radius of curvature less than the cutoff radius because the efficiency of the waveguide can diminish below 50%. The waveguide loses efficiency regardless of the angle of the bend. Any bend in prior art waveguides can induce parasitic motion which can produce heat and noise, and result in reduced component life, especially if the radius of the waveguide itself is greater than ten percent of the waveguide""s radius of curvature.
In the prior art, redirecting longitudinal motion was typically performed by either bending the waveguide, usually in a continuous curve, to the degree desired, or by exciting subharmonics and deriving use from the subharmonics. Both methods produce a superposition of motions that propagate both proximal and distal to the bend. The component of the motion not parallel to the longitudinal axis of the waveguide produces heat and noise, and can destroy the device at high powers.
Accordingly, it is a primary object of the present invention to provide a method and waveguides for changing the direction of longitudinal vibrations.
The present invention redirects substantially longitudinal motion along a first axis to substantially longitudinal motion along a second axis inclined at an angle relative to the first axis much more efficiently than prior art devices. The present invention maintains efficiency even when the waveguide has a very tight radius of curvature in the section between the two axes, and maintains efficiency over a larger angle than prior art designers typically accepted as possible without any reduction in utility. When a waveguide pursuant to the present invention redirects longitudinal motion over reduced angles similar to those used in the prior art, higher efficiencies are obtained than with conventional prior art designs. Moreover, analysis has shown that angles up to the maximum possible angle of 180 degrees can be achieved with the present invention with no restrictions on the radii of curvature. The present invention can result in transmission efficiencies near 100% at all angles even when the radius of the waveguide exceeds 10% of the waveguide""s radius of curvature. Contradicting current theory, the novel waveguide designs benefit from smaller radii of curvature, especially at larger bend angles.
The waveguides of the present invention comprise first and second half-wave sections, each having a straight portion, a curved portion and a balancing region. The half-wave sections join into one continuous piece, or are compressively loaded against each other, at the tips of their curved portions. The vibrations at the tip of the curved portion of the first half-wave section are substantially identical in magnitude and direction to the vibrations at the tip of the curved portion of the second half-wave section. The direction of vibration at the tip of each respective curved portion of each section is preferably tangential to the curve, but the present invention does not require that limitation.
In a simple embodiment, the present invention comprises two identical half-wave sections joined at the tips of their curved portions. Alternative embodiments can encompass any geometry on either half-wave section, not necessarily identical, as long as the direction of vibration of the tip of each section is substantially identical.
Slightly modifying the existing balancing features would require minor tuning to correct for higher order effects (such as a nonuniform velocity profile along the joining surfaces). The slight modification entails no gross geometric changes.
The present invention changes the direction of ultrasonic longitudinal vibrations without generating parasitic motion, heat or noise, or resulting in early failures of instruments incorporating the present invention, and can produce a tighter radius of curvature than is typically accepted as being possible in the prior art, and has potential applications in articulated ultrasonic instruments.
In accordance with the teachings herein, the present invention provides a waveguide and a method for redirecting substantially longitudinal ultrasonic vibrations along a first axis to substantially longitudinal motion along a second axis inclined at an angle relative to the first axis. First and second half-wave sections are provided, wherein each half-wave section has a straight portion, a curved portion with an end tip, and a balancing region. The half-wave sections are joined at the tips of their curved portions, and the ultrasonic vibrations at the tip of the curved portion of the first half-wave section are substantially identical in magnitude and direction to the vibrations at the tip of the curved portion of the second half-wave section.
In greater detail, the direction of the ultrasonic vibrations at the tip of each respective curved portion of each section are preferably tangential to the curve. The radius of each of the curved portions of the first and second half-wave sections can extend over a subtended angle up to the maximum possible angle of 180 degrees.
In different embodiments, two identical first and second half-wave sections are joined at the tips of their curved portions. In alternative embodiments, the first and second half-wave sections have different geometries. In one embodiment, ultrasonic vibrations produced by an ultrasonic generator are introduced into one end of the waveguide, and an end-effector cutting element is positioned at a second end of the waveguide.
Each half-wave section is designed such that the magnitude of the ultrasonic vibrations, from one end of each half-wave section to the other end of each half-wave section, has one-half of the wavelength throughout the half-wave section. The amplitudes of the ultrasonic vibrations are a maximum at one end of each half-wave section, decrease to a nodal point near the center of each half-wave section and increase again to a maximum at the tip at the opposite end of each half-wave section.
In several embodiments, the first and second half-wave sections are integrally joined into one continuous piece at the tips of their curved portions. In alternative embodiments, the first and second half-wave sections are compressively loaded against each other at the tips of their curved portions and are not integrally connected together. Moreover, the first and second half-wave sections can be rotatable relative to each other, such that the effective angle between input and output portions of the waveguide can be continuously varied.